This invention relates generally to aircraft, and more particularly, is directed to a rotary actuator for a leading edge flap of an aircraft.
It is well known to attach a leading edge flap to a fixed aircraft wing using geared rotary actuators. Such geared rotary actuators transmit torque to the flap to permit movement thereof relative to the fixed aircraft wing. In addition, such geared rotary actuators function to transmit shear loads and axial loads from the movable flap to the fixed wing, which is better capable of withstanding such loads.
However, during maneuvering of the aircraft while in flight, loads encountered by the fixed wings can be as high as nine times the weight of the aircraft. Because the wings are typically thin and are used to deflect significant amounts of air when the air loads support the weight of the aircraft during flight thereof, the loads on the wings during the aforementioned maneuvering greatly increases the deflection or bending of the wings. This bending or deflection of the fixed wings results in such excess loads being imparted to the flaps through the rotary actuators, to make the flaps conform to the deflected wing shapes. Because the flaps are typically elongated, a plurality of rotary geared actuator slices are therefore necessary to carry the loads incurred during maneuvering of the aircraft in order to reposition the flaps during such flight maneuvering.
Typically, the rotary geared actuators are manufactured from high strength steels, while the fixed wings and the flaps are manufactured from lighter weight materials, such as aluminum, titanium and composite materials which may incorporate carbon or glass fibers. Thus, because of the greater stiffness of the rotary geared actuators, they are more resistant to bending. Since the high strength rotary geared actuators do not deflect as much as the wing or flap structure, they effectively transmit concentrated loads between the flaps and the fixed wings. Therefore, in practice, such loads have been transferred by means of the mountings for the rotary geared actuators. Thus, the mounting means for the high strength steel rotary geared actuators must distribute the imposed loads to the lower strength material used in the fixed wings and flaps, and must also be able to reposition the rotary geared actuators under maneuvering air loads.
Each rotary geared actuator is comprised of a plurality of actuator slices. A conventional single slice of a rotary geared actuator is comprised of fixed and movable internal gears which surround a plurality of planet or spindle gears, which in turn, are supported by support rings and bearings and are driven by a common sun gear which, in turn, is driven through a coupling by a drive shaft. This type of rotary geared actuator forms a rugged, integral gear box capable of transmitting torque and shear loads with good torsional stiffness.
It is typically necessary to gang or connect actuator slices together to provide a structure which can carry the torque loads that are encountered. Conventionally, when the actuator slices are ganged, a common end fixed gear is used for two adjacent actuator slices. However, this construction provides that the plurality of ganged slices together form an integral unit which is stiff or rigid in the axial direction. Accordingly, it is difficult for this long, rigid actuator to conform to the bending of the wing. In addition to the aforementioned air loads, temperature changes cause axial movements of the different parts. As a result, because of the rigid nature of the rotary geared actuators, the mountings for the rotary geared actuators must allow for wing and flap deflections under load.
Typically, each rotary geared actuator is mounted to a flap and a wing through the use of tie bar assemblies which do not permit axial movement of the rotary geared actuator. Thus, as the wing bends, the rotary geared actuator cannot move axially with respect to the wing, flap or tie bar assemblies, so that the bending load on the wing is transmitted from the tie bar, to the rotary geared actuator and then to the bolts which mount the rotary geared actuator. As a result, the bolts which secure the rotary geared actuators to the wings and flaps tend to loosen, causing failure. In other words, because of the rigid, unitary construction of the rotary geared actuators and the rigid connection to the wings and flaps through the tie bar assemblies, the weakest link in the connection are the bolts which secure the tie bar assemblies to the wings and flaps, and accordingly, the first elements to fail are the bolts.
With the aforementioned known structure, the rotary geared actuators are rigidly coupled through a coupling to a drive shaft. As the respective wing bends, the drive shaft also bends, because of the rigid connection of the rotary geared actuators to the drive shaft. This bending of the drive shafts makes operation of the rotary geared actuators difficult, and induces additional stresses thereon.